The present invention generally relates to locking devices and more particularly to an improved locking device for a dental articulator with dental model casts.
To accurately form and position false teeth or caps, a dentist normally makes a negative impression of the affected tooth or teeth. The negative impression may be partial, unilateral or bilateral, depending upon the extent of work to be done; the negative impression serves as a mold for developing a die of the patient""s tooth or teeth. The negative impression is obtained by partially filling a tray with thermoplastic material. The filled tray is inserted within the patient""s mouth such that the teeth and adjacent gum sink into and create a cavity within the thermoplastic material. Shortly thereafter, the thermoplastic material will cure and retain an exact impression of the patient""s teeth and adjacent gum. This is an essentially standard technique to produce a dental cast presently used by most dentists.
Dental articulators for use with casts of a dental model to develop prosthetic dentures or denture elements have been used for a number of years. These articulators range from a very simple device affording only fixed pivotal movement between a pair of casts to highly sophisticated and mechanically complex devices which are capable of simulating the full range of occlusal and masticatory registration unique to any patient. The relatively simple devices are generally inadequate to provide sufficiently accurately registered prosthetic restoration to avoid extensive visits with a dentist to obtain adjustments thereof while the very complex devices are time consuming to operate and require extensive training to use properly. In either situation, the costs incurred to the patient are substantial. Moreover, none of the prior art articulators permit disengagement of the casts from registration with one another without extensive realignment upon reengagement. Thus, a technician is usually forced to perform his work while the casts are mounted on the articulator. Such an environment is difficult to work in with speed and accuracy. At the minimum, the vertical bite, any lateral or protrusive misalignments of the maxilla (upper jaw) and the mandible (lower jaw), and the inclinations of maxilla and mandible relative to an axis passing through the condyles when the mouth is closed have to be reproduced by a good articulator.
Each of the following listed U.S. patents are directed to dental articulators which incorporate lockable ball-and-socket elements to afford pivotal movement and extensible members to afford translational movement: U.S. Pat. Nos. 175,046; 530,524; 537,812; 565,326; 981,430; 1,736,006; 1,841,729; 2,571,280; 2,600,899; 2,608,762; 2,621,407; 2,765,533; 4,1,69,314; 4,196,518; and Belgian Pat. No. 572,850.
An articulator which provides structure to effect a simple hinged movement without provision of mechanical structure for defining translatory movement of multi-axis pivotal movement is disclosed in U.S. Pat. No. 2,430,177. Simulation of the full range of occlusal and masticatory registration is obtained by resiliently flexing the articulator. Such resiliency is afforded by the coil spring like configuration of a wire element defining each leg of two pairs of legs. For a well-trained and experienced technician, the freedom of movement afforded by this articulator is sufficient to permit the formation and adjustments of most prosthetic dentures. Accurate use of the device is predicated upon the formation of elongated sockets within each cast of a dental model for receiving, capturing and retaining each of the four wire legs. The casts usually vary in overall physical size, depending upon the size of the patient""s teeth to be simulated and the size and configuration of the base formed. To employ the articulator described in this patent, uniformity of spacing during formation of the casts is time consuming and requires an experienced technician. No adjustment capability exists within the articulator itself to accommodate differences in spacing, as would be expected, as the size of a pair of casts vary in proportion to the physical size of the patient""s jaws and the usually uniquely sized bases therefor. Other U.S. Patents describing articulators include U.S. Pat. Nos. 824,096, 3,429,045 and 3,466,750.
U.S. Pat. Nos. 4,734,033; 4,818,228; and 5,769,634 each illustrate more examples of a design for a dental articulator with a ball-and-socket joint. The limitation of these designs is that this joint is the only adjustable element allowing the upper dental cast to tilt around a horizontal axis extending through the center of the ball as well as about the vertical axis extending through the same ball. Extended range of motion is sometimes needed to accommodate a wider pool of patients. These articulators do not allow for that possibility.
It is also critical to check for any misalignment during the preparation of the dental prosthesis. In order to do so, a swinging motion is required from a dental articulator to simulate that of a human lower jaw. U.S. Pat. Nos. 4,496,320; 5,267,858; and 5,605,456 illustrate one particular element allowing for that motion. More specifically, a horizontal pin is supported by a spring and pivotally connects the upper cast to the base so that temporary dislodgment is possible to swing the upper cast to the left or to the right from the base itself. Such design allows to some approximation of the movements of the natural human jaw. However, these articulators do not afford the flexibility and range needed to accommodate most of the needs of dental patients.
The need exists therefore for a simple to use articulator which at the same time allows for a wide range of motions and accommodates an extended range of motion necessary for some dental patients.
It is an object of the present invention to provide a dental articulator with extended range of motion for maxillary and mandibular dental casts.
It is another object of the invention to provide a dental articulator allowing for quick removal and attachment of both maxillary and mandibular dental casts.
It is a further object of the invention to provide a dental articulator accurately simulating any lateral motion of the maxilla relative to the mandible.
It is yet another object of the invention to provide a dental articulator to reproduce any protrusive misalignments of the maxilla relative to the mandible.
In its preferred form, the dental articulator of the present invention has a base and a mandibular assembly extending from the front portion of the base. A vertical post extends from the rear portion of the base and pivotally supports a maxillary assembly.
The mandibular assembly comprises a mandibular plate supporting a removable mandibular base cast. The mandibular plate contains a rectangular (or otherwise non-circular) shaft extending through a corresponding opening in the front portion of the base so that the position of the mandibular assembly can be adjusted by sliding it in and out of the base. Once the desirable position is achieved, it is fixed in place by applying a set crew or other similar well-known fixation means.
The mandibular base cast of the dental articulator is provided with at least one cavity extending internally into the cast from its bottom surface. The shape of the cavity is determined by the mold forming the base cast. In one embodiment, the cavity has straight walls. In another embodiment (not shown on the drawings), the cavity is barrel-shaped. The mandibular plate is provided with an alignment structure, which includes a pair of straight-walled projections, for use in combination with the straight-walled cavity, or a pair of curved springs, for use in combination with barrel-shaped cavity. The mandibular plate is secured to the base cast by inserting and retaining the alignment structure inside the provided cavities.
The vertical post extends from the articulator base and contains a set screw so that its position can be fixed in space. The rear portion of the articulator base contains a rectangular vertical shaft adapted to be placed inside a corresponding opening in the vertical post next to a set screw. The vertical post can slide up and down that shaft for position adjustment.
The top portion of the vertical shaft contains two semi-open sockets positioned on the sides of the post and a spring-biased pin aimed at the middle between the sockets. A shaft of the maxillary support element is placed in the sockets and is retained there by the spring-biased pin. Such arrangement is by itself known in the prior art to allow for lateral motion of the maxillary assembly.
The maxillary support element contains a shaft in its rear portion for placement into the sockets of the vertical post. A separate socket is positioned in its front portion to form a ball-and-socket joint with the maxillary plate.
Maxillary assembly consists of a maxillary plate and a removable maxillary base cast. The plate contains a ball to be attached to the socket of the maxillary support element as well as the retaining structure to mate with the corresponding features of the maxillary base cast. The maxillary base cast is made in a similar manner to that of the mandibular base cast which allows for easy removal and attachment of the base cast to the corresponding plate.
The above and other objects, aspects, features and advantages of the invention will be more readily apparent from the description of the preferred embodiments thereof taken in conjunction with the accompanying drawings and appended claims.